Lampricide 3-trifluoromethyl-4-nitrophenol (TFM) impacts whole-organism oxygen consumption in non-target fishes

The application of the lampricide TFM (3-trifluoromethyl-4-nitrophenol) to streams infested with larval sea lamprey constitutes the backbone of the Sea Lamprey Control Program in the Laurentian Great Lakes, but native species have greatly varying sensitivities to TFM. Earlier work by D'Souza and colleagues revealed that the whole-animal oxygen consumption of larval sea lamprey responded in a dose-dependent manner to increasing TFM concentrations. We set out to determine 1) if TFM exposure leads to stepwise increases in whole-animal oxygen consumption in non-target fishes, and 2) if exposure to lethal TFM concentrations leads to increases in oxygen consumption comparable to the animals' Maximum Metabolic Rate (MMR). Using intermittent-flow respirometry, we tested three non-target fish species with known varying TFM sensitivity: young-of-the-year lake sturgeon (sensitive), juvenile rainbow trout (intermediate), and juvenile smallmouth bass (resistant). We confirmed that all three species exhibit increases in oxygen consumption during exposure to increasing concentrations of TFM, but found that the relationship between MMR and oxygen consumption prior to death during lethal TFM exposure is complex and species-dependent. While this complex relationship broadens the need for species-specific testing, it opens up interesting possibilities both for (1) in-situ testing, e.g., through the deployment of river-side field respirometry systems to monitor real-time responses of both target and non-target species to TFM treatments, and (2) ex-situ testing, e.g., through the establishment of less-lethal assays to determine TFM sensitivity under various species × temperature × water chemistry combinations.